William f



Aug. 5, 1924. 1,504,139 W. F. R. PHILLIPS DIAPHRAGM Filed Sept. 16 1921INVENTOR.

ATTORNEY.

Patented Aug. 5, 1924.

UNITED STATES WILLIAM F. R. PHILLIPS, OF WASHINGTON, DISTRICT OFCOLUMBIA.

DIAPHRAGM.

Application filed September 16, 1921. Serial No. 501,026.

To (ZZZ whom it may concern:

B; it known that I, VVILLIAP-I F.

Z-TILLIPS, a citizen of the United States, residing at lVashington,District of Columbia, have invented new and useful Improvements inDiaphragms, of which the following is a specification.

This invention relates to a vibratory diaphragm for talking machines andother sound reproducing instruments, the dominant resonating element ofwhich is wood, that is, it is a diaphragm that is essentially a woodendiaphragm as. to its dominant resonating properties and qualities,though the diaphragm is not necessarily .wholly of wood, but may-consistof wood reinforced for the purpose of mechanical s"curit v with somemembranous material, such as paper, parchment, celluloid, or othersubstance existing in or wrought into membranous condition. V

The resonant properties and qualities of wood are well known and the useof wood as a resonator in musical instruments and in talking machines isnot claimedas new. )Vooden diaphragms for talking instruments made ofsingle continuous discs cut in the usual manners of cutting wood, thatis quartered, bastard or transverse, (or cross grain), are notsatisfactory because of interfeieuces in wave motion that result fromth" natural structure of wood as found in discs cut as described. Oneexception is to be noted. namely, if a disc were to he cutcross grainand the section should contain the pith or marrow so located as to be atthe center of the disc, such a disc would have a natural arrangement ofthe wood that will not gi e rise to interferences in wave motionoriginating at the center of the disc. So far as known no one hash-retofore recognized this fact and it is therefore claimed as includedin this invention, either unmodified or modified as hereinafterdescribed. The invention in the matter of wooden diaphragms forreproduction of sound in talking machines and instruments, and for shorthereinafter unless otherwise stated the term diaphragm only will beused, will be more readily understood b v first stating briefly thestructural pecularities of wood and how these peculiarities affect Wavemotion in diaphragms made of single pieces of wood cut. in the usualplanes in which timber is cut, namely. quartered, (Fig. 7), bastard (notillustrated), or cross grain F ig. 8). Using the term in its commonsense. wood is mad. up of two different parts, spring Wood and summerwood arranged in concentric alternating rings, the annual rings (Figs. 7and 8) around the pith or marrow of the tree, easily seen as such inmost Woods cut transversely of the long axis of the tree. When outlengthwise of the tree in the manner known as quartered the spring andthe summer woods appear as lines or hands of lighter and darker colorsrespectively. In quartered wood these bands or lines are quite regularin arrangement and appearance, and generallythe spring wood is thebroader of the two. In bastard cuts the width of the linesor bands andtheir relations to each other and their directions are apparently veryirregular, sometimes more spring wood sometimes more summer wood beingin evidence, according to the surface considered. Biologically thespring wood and the summer .wood are alike. Physically the summer woodis the heavier or denser and the spring wood the lighter or less dense.If there be any difference in the elasticity of the two it appears (sofar as I am advised) not yet determined: biological considerations wouldseem to indicate that there is none. The densities being known to beunequal, it follows that the velocit of wave motion in the two sorts isdifferent, the velocity being in any medium proportional to the squareroot of the modulus of elasticity divided by the density of the medium.

In a disc made of quartered wood. (for example like Fig. 7) in thedirection of the grain, that is that of the lines or hands of the summerand spring woods, a wave frontwould travel, be it in either the springwood or the summer wood, in a medium relatively homogenous in structureand density, and its speed would be uniform. On the other hand, a wavetraveling perpendicularly to the grain, Would be passing through amedium alternately varying in density, and the wave would be subjectedto retardations and reflections at every variation of density; its speedwould not be uniform, and its intensity or force would be decreased. Awave traveling diagonally across the grain would ex erience the sameconditions but the quantitive effect would be dependent on the angle ofincidence made with the bands of varying density. In disc made ofwoodcut cross-grain. (as for example Fig. 8) except in a disc mad ofsuch a section having the pith as its center, the same generalconditions would obtain as in one cut of quartered wood. A disc made ofbastard cut wood would be subiect to the same general conditions, onlyin a more irregular and uncertain degree.

In discs of wood cut in the manners mentioned. the exceptionnotedexc'epted, waves initiated at the center of such discs would travelnot circularly,but more or 1 ss ellip' tically, or as ellipt'oids. Insound repro du'oin'g diaphragms Q-made of any of the discs abovementioned (except thebne illustrated in Fig. 4) the major part of thewave would be reflected back to the center in a very complex form, whichmay be roughly said to be ellip toidal, with the long: axis of thereturn wave at right angles to that of the original wave; altogether,the elliptoidal form of the original wave, the complex form of thereturn wave, the numerous asymmetrical refi c tions due tt) theasymmetry of the grain to the center, give rise ,to many inter ferencesin wooden} diaphragms of single pieces of wood, tlie's-i-ng'le exceptionabove noted excepted.

Briefly this is why ordinarily the ,"forms in which wood is (int,arc'unsuited ,to be Fig. 1 is a cross'secti'on of a sini 1e, form ofdiaphragm 'I'nad'ofwood, and aving'a papr or'Tothei' membranous a cifigfand backing, either one of which'canbe omitted.

In'thjs' figure. the aggerated. Fig is asimpl' I built-up diaphragm,composed of our wooden sectors, cut quartered, the grain running atright angles tofthe central radius this being the 'a'xi'sjof' symmetf ofeach sector. Fig; 3, shows a; similarly con structed diaphra m, withthegrainparallel to the central radius eah'sectqr, Fig. 4 shows a crosscut ,dia raglfn, riiade ofon aper ng masses is x piece. the pith of thetr e'e a t 'the 'cent'er of the c iaphrag'm. Fig? 5.'show s a built-upphra'g'm simulating that shown in Fig. 4 throu 'h the mediuniofthe"central .pin or Stj'il'lr; holder. Fig. 6. slioii'foti. mode ofmounting the diagrams on the sound box. Figs. 7 and 8 show respectivelydiscs of quartered wood and cross cut (ordinary or none'centra'l) woodThese latter mak unsatisfactory diaphragms for the! reasonsabot'eset"fortli l V i i The diaphragm isa thin, circular disc. whollyof wood"or formed of wood and membrane, such as paper. parchment,celluloid, or other m'ateiial already alluded to. The diaphra m is showndiagrammatically the wooden portion thereof being in perpenf m f 2dicular medial section in Fig. 1, indicated by the numeral (4). Thesmall central projection (5) is a Wooden peg or piirfor attaching theactuating end of the needle lever to the diaphragm, and is designatedthe union. The thickness of the diaphragm varies somewhat according toits diameter and the manner of the construction of the diaphragm itself.Generally the thickness may be about 1/32 inch at its center and notsubstantially more than 1/100 inch at the periphery. Wood diaphragmshaving a maximum thickness of less than 1/64 of an inch, seem to losethe peculiar tonal properties that make wood desirable as a reproducingdiaphragm.

In practice, diaphragms appear to give better results if thicker'in thecenter than at the periphery. In the diaphragms herein described ,thecentral part is always the thickest and the periphery the thinnest.Between these two parts, the thickness diininishes either gradually anduniformly, or uniformly and more or less gradually, producing either aninclined plane, a convex, or a concave surface, or surfaces, or any de--sired combination of them. No one shape seems to be better thananother, but a planoinclined surface as contra a plano-concare orplano-conrex, is contemplated. Thus the preferred form of constructionof the diaphragm is that of a very flat cone.

The wood of which the diaphragm may be made, in whole or in part, may beofany kind, but soft woods, and particularly soft and brittle woods,such as white pine, cedar. balsa and fold field piped, (a short leafpine which is cheapiand abundant, and commonly used for making lightpacki ng boxes), also .called loblolly pinc in some localities have beenfound to ire particularly good results. These woocs are generally soft.quite brittle, and are quite generally avail able. They area'elativelyhonaogeneous in structure, the ,yariation in density. betweenthe softenpartfandthe harder part of the annual rings is low, ascompared with other kinds of wood, and they possess excellent tonalqualities.

Soft, but relatively tough woods. such as spruce, do not appear topossess the resonant qualities of the soft and brittle woods. and arenot well suited for sound box diaphragms.

Awood diaphragm of the thinness and of the kinds of .WOOd described mybe easily damaged, split or broken, by careless ban dling, particularlyby splitting in the direc tion of the grain of the wood. Such accidentsmay be minimized without impairing apparently the resonant qualities ofthe diaphragm by facing one or both of its surfaces with some thinfibrous paper. such as onion skin paper. or by a thin film of el luloidor parchment, or other membranous material of equivalent thickness ortenacity. as shown in Fig. 1. Also wood being to a limited degreehygroscopic, and its resonant quality being impaired by an excess ofabsorbed moisture, facing the diaphragm on one or both sides inhibitsundue absorption of atmospheric moisture. Furthermore, efficientwaterproofing may be applied to the paper or other membrane withoutimp-airing the resonant quality of the wood, something diilicult to dowhen the waterproofing is applied direct to the wood. When a membrune(paper or the like) is not applied to the front side of the woodendiaphragm, this may be given a light coating of a suitable varnish. andit is preferred that this be applied superficially, as much as possible,since an impregnation of the woodwith varnish, or the like, is injuriousto its tonal qualities.

The diaphragms to be hereinafter described in more detail, willtherefore be fared on one or both sides for the purposes indicated. andwhen so faced the membranous facing becomes an integral part of thediaphragm and continues it in extent, forming an annular ring ofmembranous material of determinat width, around the wooden portion. Thediaphragm is secured to its support through this membranous ring.

The diaphragms shown in Figs. 2, 3, and 5 are each made of four or moreSee'- tors cut and joined by glue or other 06- ment so as to give anapproximate concentric arrangement of the grain withinthe disc area.This symmetrical ordering of the grain obtained by this arrangement,insures far more uniformity of resistance to pressure in all diametersand consequently more uniformity of vibrating movement of the diaphragm.Obviously the uniformity approaches the limit of absoluteness as thenumber of the sectors is increased. However. in practice no appreciableimprovement is noticed beyond six or eight or ten sectors. Diaphragms ofthis type reproduce satisfactorily all kinds of phonographic recordsseemingly with perfect fidelity to the original :is recorded on thephonograph disc.

The diaphragm shown in Fig. 4 is made by cutting the wood transverselyas in Fig. 8, but the section is cut from the heart region of the woodand has as its own center the natural center of the wood. therefore asperfect uniformity of grain is thus obtained as is practicable.

In wood diaphragms built up of'sectors, the invention is not restrictedto the use of a particular number of such sectors. In those shown in Figs. 2, 3 and 5. the sectors are attached to each other, and to theunion or pin 5 preferably by a suitable gtue' or cement. Ordinarycarpen'ters glue can be employed. It will be clear that the greaternumber of sectors, the more closely absolutely the finished diaphragmshould approach absolute uniformity if the cement or glue used inattaching each sector to its nei hbor. were. absolutely homogeneous witithe wood. However, the two are not homogeneous with each other, andordinarily the use of more than eight or ten sectors is notadvantage-ous- Obviously, no excessive amounts of glue are to be used,since as above stated, it is not desired to impregnate the wood 'Withany foreign substance.

The diaphragms shown, Figs. 2. 3. 4 and 5 are of wood faced on one orboth surfaces with paper, celluloid, or parchment, or other membranousmaterial.

Fig. 6 shows the relation between the wooden portion and the membranousportion of the diaphra m, seen either from the front or back. In thisfigure, 5 is the union or connecting pin, 13 is the wooden disc, 14 isthe inner'margin of the funnel of the sound box, 16 is its outer margin,the membranous portion of the diaphragm uncovered by the wooden portionextends laterally from 13 to 16.

Referring again to Fig. 4 of the drawing, if a cross-grain section ofwood that in cludes the pith or marrow be taken and a disc cut/from itso as to have the pith as the center, it will be seen that the springarid summer Woods are substantially symmetrically disposed about thecenter. If pains be taken in selecting the wood the degree of symmetrycan be brought very near absolute. A wave initiated at the center of acarefully selected disc will be subject to retardations and reflectionsdue to the alternate variations in density of the spring and summerwoods. However these retardations and-reflections will be symmetrical.in all radii, and therefore interferences will. not occur. The wave willadvance from and return to the center as little interfered with in form,as if in a homogeneous medium.

A diaphragm fashioned with respect to the grain and pith as abovedescribed and shown in Fig. 4, is original so far as relates todiaphragms for sound reproducing machines. The other diaphragms shown inFigs. 2, 3. and 5, are approximations of this symmetry.

The fundamental princi le involved in making a workable Wooden diaphragmmay be stated as radial symmetry in the disposition of the grain.

By radial symmetry as herein applied to wooden dia hragms is meant anyarrangement of the grain of the wood about the center of the diaphragmwhereby the grain of the wood will be so balanced with respect to thecenter of the diaphragm that any and every radius shall hold. (Withinlimits indicated herein) with respect to any and every other radius withwhich it may be compared, the same relation to the grain 1 of the woodThat is, if one radius is perpendicular to the grain or to the cord ofthe arc of the concentric rings, every other radius is and thisconstitutes the preferred construction.

I propose to construct diaphragms of sectors cut from quartered wood,and to arrange them either so that the grain shall be concentricallydisposed around the center, as in Fig. 2. The specification of diaphragms made of 4 to 10 sectors, is not to be understood as limiting thenumber, but I may avail myself of whatever number may be deemed mostsuitable either with respect to the size of the diaphragm or the qualityof the wood used, or both.

Experiments have demonstrated that in diaphragms in which the wood, isarranged as above described, wave motions initiated at the center willbe propagated more or less circularly and symmetrically and will be freefrom the interferences inherent in wooden diaphragms constructed ofsingle pieces, the exception above noted excepted.

A diaphragm for talking machines to be commercially valuable, should-becapable of reproducing most of the phonographic records on the market.To meet this re uire-i ment the diaphragm must have the astic qualitiesof the diaphragms making the recorder for which the record is :made;--The effective vibrating surface ofdiaphragms in use, isbetween 13/4and 2 inches. A wooden diaphragm constructed of sectors as abovedescribed, the wood used being white pine, and having an effectivediameter of 2 inches, to be capable of reproducing the record asperfectly as recorded .is

found to weigh .less than 40 milli ams, the.

best results being obtained wit aone in which. the weight of the woodasfi'nally finished was 35 milligrams. :A wooden 'disc made up" of eightwhite pine sectors 2-1/4 inches in diameter; the size necessary to secure the periphery to the sound box rim.

which weighed 37 milligrams, was found'to be about 1/64 inch thick atthe center andto taper to less than 1/100 at the periphery. Such a discis too fragile for the usage to which a talking machine diaphragm issubjected. However, adiaphragm ofthis description can be made strongenough to with stand the ordinary usage to which subjected byreinforcing it with some tough but light membranous material, such asonion skin or other thin, tough paper, celluloid, vegetable parchment,or other similar light and tough membranous material. In practice I haveused thin onion skin or similar paper impregnated with thin celluloidvarnish. Such a membrane is very light, strong and thin, being not over.002 of an inch thick. lVhen a wood diaphragm as described is reinforcedby being mounted on a membrane made of such paper, it is practicable todispense with so much of the wood as might extend upon the rim of thesound box, replacing it by extending the membrane thereon. In actualpractice better results have been obtained by still further reducing thediameter of the wooden disc. A wooden disc of 1-3/4 inches mounted on amembrane of paper and varnish as above described. thus giving in a 2inch diaphragm a membranous margin of 1/8 inch inside the rim of thesound box is a very satisfactory diaphragm. I therefore propose to somount any, and all, of the wooden diaphragms herein described. The abovedimensions are given by way of illustration only. The woods of which lpropose to make these diaphrngms may be of any kind, but in practice. Iprefer white pine and have obtained very satisfactory tonal results fromit. Next to white pine, I have found selected pieces of loblolly or oldfield pine very satisfactory. Cedar, yel low pine and balsa. have alsogiven good results.

Comparing wood with membrane such as paper, parchment, or celluloid, forequal Weights, the membrane will be found the stronger in mostdirections. Now experiment shows that as already stated wood has themost suitable tonal qualities as a general reproducing medium;experiment shows also'that' membranes such as mentioned are deficient intonal qualities. A paper combination' of wood and of membrane,therefore, seems to be the desideratum. In the diaphragm shown in Fig.7, this end is sought to be obtained.

It appears advisable in most cases, not to employ excessive amounts ofpaper or membranous materials. One thickness or atmost two of such paperas onion skin (say on the outside) with the other side of the wooduncovered (or preferably coated with an extremely thin coat of awaterproofing agent, such as shellac), gives better results than athickness of paper on both The preferred construction is to employ thesmallest amount of wood necessary to give the optimum tonal quality. Anexcess of wood seems to slow down the vibrations and hence toreduce thevolume of sound. Several thicknesses of paper have a like effect, tosome extent, and also will reduce the tonal quality to a greater degree.

I claim:

1. Adiaphragm comprising a wooden disc constructed of not less than fourwooden sectors, the sectors equal in size and the grain of the wood ofevery sector perpendicular to the axis of symmetry of the sector; thiswooden disc being attached to and reinforced by a thin membranous disc,of

material of approximately the thickness of onion skin paper, suchmembranous disc being of a greater diameter than the wooden disc,whereby the completed diaphragm shows a central wooden disc surroundedby a membranous margin of a determinate width.

2. A diaphragm built up of not less than four sectors of the same size,the grain of the wood being symmetrically arranged in each of saidsectors, and said sectors being joined to each other by a cementingmaterial and having the grain of the wood approximately at right anglesto the radius of symmetry of the sector as hereinbefore described.

3. A diaphragm comprising at least four wooden sectors having the grainapproximately radially symmetrically disposed around the center of thediaphragm in such manner that the grain is substantially perpendicularin each sector to the axis of symmetry of the sector.

In testimony whereof I afiix m signature.

WILLIAM F. R. P LLIPS

